Pondus
2
what AV did you have before installing avast ?
have you removed it ?
have you run a removal tool to clear any leftovers ?
run and reboot - Uninstallers for Security Software
http://thewebatom.net/uninstallers/security-software/
If still problems try avast repair and reboot
For a repair of avast. Windows, Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button from the pop-up window, scroll down to Repair, click next and follow.
or a complete new install using this http://www.avast.com/en-us/uninstall-utility